1. Field of the Invention
This invention relates to a motor operator for opening or closing contacts of pad-mounted switchgear adapted for use in high voltage underground distribution systems. Drive components of the operating mechanism are constructed in such a fashion that the overall size of the motor operator is relatively compact and may be readily mounted as a retrofit unit on the side of an existing switchgear cabinet. The motor of the operator may be activated either locally or remotely to open or close the contacts; alternatively, a drive element normally coupling the motor to the contact operating shaft is selectively removable so that a wrench may be used to manually open and close the contacts when necessary. Removal of the drive element substantially precludes accidental injury during use of the wrench if the motor is unintentionally actuated.
2. Description of the Prior Art
Underground electrical transmission and distribution systems include a main service line leading from a substation with a number of individual distribution lines connected in parallel to the main line at strategic points along the length of the latter. It is often the practice, particularly where power is supplied to a user entity such as a shopping center or discrete residential development to provide padmounted switchgear in each of the lateral distribution lines connected to the main in order to allow selective de-energization of that lateral distribution line without the necessity of de-energizing all of the lateral distribution lines because of the service main. Switchgear apparatus conventionally includes electrical, movable contacts which may be opened and closed by maintenance personnel, as well as fuse structure which protects the line from the influence of high or low level faults that may occur in one of the branch laterals. In a particularly useful type of switchgear, vacuum switches are employed for circuit control and which are mounted under oil along with the fusing structure to minimize the overall size of the switchgear housing.
Generally, the vacuum switch contacts of padmounted switchgear as described require snap action opening and closing mechanism to minimize arcing and assure a positive closing of the switch contacts. Actuation of the switch operating mechanism is normally accomplished by hand. In some cases, however, motor operators have been installed within the switchgear cabinet for powered actuation of the opening and closing mechanism. Recently, there has been increased interest in switch contact actuating mechanism that is motor operated and can be activated at remote locations as well as locally by a switch within the cabinet.
Certain of the known switchgear motor operators are relatively bulky, however, and are adapted to be installed only within the main housing or cabinet of the switchgear. By design, these units are not suitable for installation on a retrofit basis on an external side of an existing switchgear cabinet. Moreover, most of the available motor gear operators are relatively expensive, both in terms of cost for the various components as well as the expenses for installation of the same. Furthermore, these units do not readily lend themselves to manual actuation in the event of motor failure or in the event the operator desires to open the switch contacts by hand. Hence, there is a need for a motor operator which overcomes these and other problems associated with known devices.